Check out Tim's Video
about glass. He demonstrates how tough glass from different companies. Honestly, I've been disappointed in my phallix purchases recently. Every time I get one the heads on them are so much smaller then they should be. Check out my comparison image. The Cobalt one has the perfect head shape, but the other two are just too small. If you want a popping sensation, you want a fuller head. I've never had a quality issue with any of the other glass companies. I own 30 glass pieces. And phallix is the only company slipping.